Information technology and data handling systems commonly use data protection technology to defend against unexpected catastrophic events. Backup systems are a first line of defense against disaster. A second line of protection is mirroring systems, fault-protection systems for organizations that use tape drives for backup and recovery. A mirroring system creates a mirror copy of a backup session, doubling protection by enabling storage of identical backup records in different locations. A tape mirror gives backup and recovery protection by creating a mirror or virtual tape drive, generating two or more physical tape devices that appear as one unit in the mirror and operating in conjunction with existing backup software to write identical backup data to each tape drive in the mirror simultaneously.
A user often desires multiple copies of the same tape, written at the same time, for several reasons. A user may wish to store one copy of the backup tape onsite for fast data recovery and maintain a second copy offsite to protect against site-wide disasters. The user may desire a fail-over capability to increase the success rate of backups. The user may also desire a redundant system that creates multiple tape media copies for restoration purposes in case one copy of the media degrades or fails.
Some data protection software can create multiple tape copies by generating a first backup media, then copying a second tape from the first. A difficulty with the procedure is that any data corruption in the original backup tape media is duplicated on the second copy. Furthermore, the making of serial copies is time consuming. The time to create a second copy can be as long as the time to create the original backup. During the copy operation, both the original and duplicate backup copies are on line so that are susceptible to destruction, along with the originating system, during a site-wide disaster.
Tape mirroring can be used to generate a copy of a backup tape while the backup job is running. Tape mirroring techniques include software mirroring, for example utilizing software executing in a tape driver, and hardware mirroring, for example commonly functioning in a tape library. In either case, any write operation to a primary tape backup is concurrently mirrored to a second copy. In a mirrored backup, no time delay is incurred during creation of the second tape copy due to concurrent creation of the multiple copies.